Cast Clever Impersonator by paying its mana cost. Choose to have it enter the battlefield as a copy of Ao.
Put Clever Impersonator into your graveyard due to the legend rule.
When Clever Impersonator dies, it and Mortuary trigger.
Resolve the Mortuary trigger, putting Clever Impersonator from your graveyard onto the top of your library.
Resolve the Clever Impersonator trigger, causing you to look at the top seven cards of your library and put Clever Impersonator onto the battlefield as a copy of Ao.
Repeat from step 2.

Infinite creature LTB

Infinite creature ETB

Infinite death triggers

Ao, the Dawn Sky

Mortuary

Clever Impersonator

Activate Phyrexian Altar by sacrificing Ao, adding one mana of any color.
Ao dies, triggering itself and Nim Deathmantle.
Resolve the Ao trigger, putting four +1/+1 counters on each creature and Vehicle you control.
Activate Workhorse by removing four +1/+1 counters from it, adding {C}{C}{C}{C}.
Resolve the Nim Deathmantle trigger, causing you to pay {4} to return Ao from your graveyard to the battlefield, and then attach Nim Deathmantle to it.
Repeat.

Infinite +1/+1 counters on most creatures you control

Infinite +1/+1 counters on all Vehicles you control

Infinite colored mana

Infinite colorless mana

Infinite creature sacrifice triggers

Put a selection of permanent cards from your library onto the battlefield

Workhorse

Nim Deathmantle

Phyrexian Altar

Doubling Season

Vorinclex, Monstrous Raider

Combos with "Ao, the Dawn Sky"